Optical information recording medium and recording method using the same

ABSTRACT

An optical information recording medium  10  includes a first substrate  11 , a second substrate  12  disposed in parallel with the first substrate  11 , and an information layer  20  disposed between the first substrate  11  and the second substrate  12 , and the information layer  20  includes a recording layer  23  and inorganic layers (lower side interface layer  22  and upper side interface layer  24 ) adjacent to the recording layer  23 . The recording layer  23  is changed between at least two different states, which are discernable optically, by irradiation with a laser beam  14  incident from the first substrate  11  side. The inorganic layer contains a nitride of Si x Ge 1-x  (where 0.3≦x≦0.9) as a main component. The present invention provides an optical information recording medium capable of recording/reproducing information with satisfactory reliability even in recording/reproducing with a light beam having a short wavelength or in recording/reproducing with respect to a plurality of information layers.

TECHNICAL FIELD

The present invention relates to an optical information recording mediumcapable of recording/reproducing an information signal by irradiationwith a light beam such as a laser beam and a recording method using thesame.

BACKGROUND ART

Conventionally, it is known that a thin film made of a chalcogenmaterial or the like formed on a substrate is locally heated byirradiation with laser light, whereby a phase can be changed between anamorphous phase and a crystal phase having different optical constants(refractive index n, extinction coefficient k), using differentirradiation conditions. A so-called phase-change type opticalinformation recording medium using the above phenomenon is being studiedand developed actively. In the phase-change type optical informationrecording medium, an information track of the recording medium isirradiated with a laser beam whose output is modulated between two powerlevels: a recording level and an erasure level, whereby a new signal canbe recorded while a previous signal is being erased. Generally, in sucha recording medium, a multi-layer film including layers other than arecording layer is used as an information layer for recordinginformation. For example, a multi-layer film including a protectionlayer made of a dielectric material or a reflection layer made of metalcan be used as the information layer.

The protection layer made of a dielectric material has, for example, thefollowing functions of

(1) protecting a recording layer from mechanical damage from outside;

(2) reducing thermal damage occurring in the case where a signal isrewritten repeatedly to increase the rewritable number of times;

(3) enhancing the change in optical characteristics by using aninterference effect due to multi-reflection; and

(4) preventing a chemical change due to the influence of outside air.

As a material for the protection layer achieving the above-mentionedobjects, conventionally, an oxide such as Al₂O₃, TiO₂ and SiO₂; anitride such as Si₃N₄ and AlN; an oxynitride such as Si—O—N; a sulfidesuch as ZnS; and a carbide such as SiC are proposed. Furthermore, as thematerial for the protection layer, a material such as ZnS—SiO₂ that is amixture of ZnS and SiO₂ also is proposed. Among these materials,ZnS—SiO₂ has a considerably small thermal conductivity among thedielectrics, and can minimize the heat diffusion occurring duringrecording with a laser beam. Therefore, the recording sensitivity isenhanced by using ZnS—SiO₂. Furthermore, due to a small internal stress,even when this material is formed into a thick film, cracking isunlikely to occur. This material has high adhesion with respect to aphase-change material layer, so that the film made of such a material isunlikely to peel off even after repeated laser irradiation. For thesereasons, ZnS—SiO₂ mostly is used as the material for the protectionlayer.

Furthermore, an interface layer between a recording layer and adielectric layer is proposed. The interface layer has, for example, thefollowing functions of:

(1) promoting the crystallization of the recording layer to enhanceerasure characteristics; and

(2) preventing mutual diffusion between the recording layer and theprotection layer (dielectric layer) and enhance durability in repeatedrecording. The interface layer also needs to have characteristics inwhich corrosion and peeling from the recording layer are not likely tooccur.

As the material for such an interface layer, for example, a nitride ofSi or Ge is disclosed (see JP 5(1993)-217211 A and WO 97/34298). Thesematerials are very excellent in the above-mentioned crystal coregeneration promoting effect and diffusion preventing effect. However, itis reported that due to the insufficient adhesion with respect to therecording layer, the interface layer made of Si—N peels off underhigh-temperature and high-humidity conditions, and thus, the reliabilityduring long-term use is low (see WO 97/34298). In contrast, an interfacelayer containing Ge—N as its main component is unlikely to peel off evenunder high-temperature and high-humidity conditions, and thus, Ge—N isone of the most suitable materials for the interface layer. WO 97/34298shows that Cr or the like is effective as an additive to Ge—N in termsof moisture resistance. Si also is listed as an example of an additive.However, WO 97/34298 does not disclose the amount of Si added to Ge—Nand specific effects obtained by adding Si.

In the above-mentioned recording medium, as basic means for increasingthe amount of information that can be accumulated in one medium, thereis a method for shortening the wavelength of laser light or increasingthe numerical aperture of an objective lens condensing the laser light,thereby decreasing the spot diameter of laser light and increasing thedensity of a recording surface. Furthermore, in order to increase therecording density in a circumferential direction, mark edge recording isintroduced in which the length of a recording mark is information.Furthermore, land and groove recording is introduced in whichinformation is recorded on grooves for guiding laser light and landsbetween the grooves, so as to increase the recording density in a radialdirection. Furthermore, the recording density can be increased even byusing a plurality of recording layers. A recording medium including aplurality of recording layers and a recording/reproducing method thereofhave already been disclosed (see JP 9(1997)-212917 A, WO 96/31875, JP2000-36130 A). Furthermore, layer recognizing means and layer switchingmeans are disclosed for recording/reproducing information by selectingone recording layer from a plurality of recording layers (see WO96/31875).

In a recording medium (multi-layer recording medium) including aplurality of information layers, an information layer closer to a laserlight source absorbs light. Therefore, an information layer far from thelaser light source records/reproduces information with attenuated laserlight. This causes a decrease in sensitivity during recording and adecrease in reflectance and amplitude during reproducing. Thus, in themulti-layer recording medium, in order to obtain sufficientrecording/reproducing characteristics with a limited laser power, it isrequired that the transmittance of the information layer closer to thelaser light source is increased, and the reflectance, difference inreflectance (difference in reflectance between a crystal phase and anamorphous phase) and sensitivity of the information layer far from thelaser light source are increased.

Recently, a violet laser diode having a wavelength in the vicinity of400 nm is being put into practical use. Then, an attempt is made toincrease the density of a recording surface by applying the laser diodeto a light source of a recording apparatus for an optical informationrecording medium. However, the spot diameter of a laser beam isdecreased as the wavelength becomes shorter, and hence, the energydensity of the laser beam is increased. Because of this, each layer ofthe information layers is likely to be thermally damaged duringrecording. Consequently, in the case of a number of repeated recordings,recording/reproducing characteristics are likely to be degraded.Furthermore, in general, the light absorption of the dielectric materialis increased and the transmittance thereof is decreased as thewavelength becomes shorter. Therefore, when the wavelength of a laserbeam is short, for example, the transmittance of an information layer inthe multi-layer recording medium closer to a laser light source isdecreased, and a laser beam with a sufficient power cannot reach theinformation layer far from the laser light source. Furthermore, sincethe light absorption is increased in the interface layer, the lightabsorption in the recording layer is decreased, which results in adecrease in recording sensitivity.

In the case of using an interface layer containing the above-mentionedGe—N as a main component, characteristics hardly are degraded even whenrecording is repeated a number of times in recording/reproducing using alaser diode with a red wavelength. Furthermore, the extinctioncoefficient k of the interface layer at a red wavelength is small (i.e.,0.05 or less), whereby a high transmittance can be ensured. However, theinterface layer is likely to be thermally damaged as described above ata violet wavelength. Therefore, the interface layer is degraded due torepeated recording. Furthermore, the extinction coefficient k at aviolet wavelength is large (i.e., about 0.2), which makes it difficultto ensure a high transmittance.

DISCLOSURE OF INVENTION

In view of the above circumstance, the object of the present inventionis to provide an optical information recording medium capable ofrecording/reproducing information with high reliability even inrecording/reproducing with a light beam having a short wavelength or inrecording/reproducing with respect to a plurality of information layers;a producing method thereof; and a recording method thereof.

In order to achieve the above-mentioned object, an optical informationrecording medium of the present invention includes: a first substrate; asecond substrate disposed in parallel with the first substrate; and aninformation layer disposed between the first substrate and the secondsubstrate, wherein the information layer includes a recording layer andan inorganic layer adjacent to the recording layer, the recording layeris changed between at least two different states, which are discemableoptically, by irradiation with a light beam incident from the firstsubstrate side, and the inorganic layer contains a nitride ofSi_(x)Ge_(1-x) (where 0.3≦x≦0.9) as a main component. Due to highthermal stability, the inorganic layer can enhance the durability inrepeated recording and the environment reliability such as moistureresistance. In particular, in the case of recording with light having ashort wavelength such as a violet laser, by increasing the content ofSi, i.e., setting 0.3≦x, heat resistance is enhanced, and satisfactorydurability in repeated recording can be obtained.

The above-mentioned recording medium further may include at least onemore information layer disposed between the first substrate and thesecond substrate. According to this configuration, recording withparticularly high density can be performed. Furthermore, due to arelatively small extinction coefficient k, the inorganic layer canenhance the transmittance and the recording sensitivity of a multi-layerrecording medium. For example, the extinction coefficient k at awavelength of 405 nm of the inorganic layer satisfying 0.3≦x can be setto be 0.15 or less.

In the above-mentioned recording medium, the recording layer may bechanged reversibly between the at least two different states, which arediscernable optically, by irradiation with the light beam.

In the above-mentioned recording medium, a wavelength of the light beammay be 500 nm or less.

In the above-mentioned recording medium, the information layer mayinclude a reflection layer disposed on the second substrate side withrespect to the recording layer.

In the above-mentioned recording medium, the recording layer may be madeof an alloy containing Te and Sb.

In the above-mentioned recording medium, a thickness of the recordinglayer may be 18 nm or less.

In the above-mentioned recording medium, the recording layer may be madeof a Ge—Sb—Te based alloy, a Ge—Sn—Sb—Te based alloy, an Ag—In—Sb—Tebased alloy or an Ag—In—Ge—Sb—Te based alloy.

In the above-mentioned recording medium, the recording layer may be madeof a Ge—Sb—Te based alloy, and the alloy may contain Ge in a content of30 atomic % or more.

In the above-mentioned recording medium, the recording layer may be madeof a Ge—Sn—Sb—Te based alloy, and the alloy may contain Ge and Sn in acontent of 30 atomic % or more in total.

Furthermore, in a first method for recording information onto an opticalinformation recording medium including a recording layer and aninorganic layer adjacent to the recording layer, the inorganic layercontains a nitride of Si_(x)Ge_(1-x) (where 0.3≦x≦0.9) as a maincomponent. When the recording layer is irradiated with pulse lightmodulated between a power level P1 and a power level P3 smaller than thepower level P1 to be changed to a state having different opticalcharacteristics, thereby forming a recording mark, the number of pulsesof the pulse light is increased as the recording mark is longer, and avalue of P3/P1 is increased as a linear velocity of the opticalinformation recording medium is higher.

Furthermore, in a second method for recording information with respectto an optical information recording medium including a recording layerand an inorganic layer adjacent to the recording layer, the inorganiclayer contains a nitride of Si_(x)Ge_(1-x) (where 0.3≦x≦0.9) as a maincomponent. When the recording layer is irradiated with pulse lightmodulated between a power level P1 and a power level P3 smaller than thepower level P1 to be changed to a state having different opticalcharacteristics, thereby forming a recording mark, the number of pulsesof the pulse light is increased as the recording mark is longer. Whenthe recording mark is erased by irradiating the recording mark withcontinuous light of a power level P2 between the power level P1 and thepower level P3 , a value of P3/P2 is increased as a linear velocity ofthe optical information recording medium is higher. According to thefirst and second recording methods, even in the case where a recordingmedium is stored under high-temperature and high-humidity conditions, adecrease in a signal amplitude of a recording mark and difficulty inerasing a recording mark can be prevented.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a partial cross-sectional view showing an example of anoptical information recording medium of the present invention.

FIG. 2 is a partial cross-sectional view showing another example of theoptical information recording medium of the present invention.

FIG. 3 schematically shows an example of a recording/reproducingapparatus used for recording/reproducing in the optical informationrecording medium of the present invention.

FIG. 4 shows an example of a pulse wavelength of a laser beam used forrecording in the optical information recording medium of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described specifically by wayof embodiments with reference to the drawings.

Embodiment 1

In Embodiment 1, an example of an optical information recording mediumof the present invention will be described. FIG. 1 shows a partialcross-sectional view of an optical information recording medium 10(hereinafter, which may be referred to as a recording medium 10) ofEmbodiment 1.

As shown in FIG. 1, a recording medium 10 includes a first substrate 11,a second substrate 12 placed in parallel with the first substrate 11,and an information layer 20 placed between the first substrate 11 andthe second substrate 12. In the recording medium 10, information isrecorded and reproduced with a laser beam 14 incident from the firstsubstrate 11 side through an objective lens 13. The wavelength of thelaser beam 14 is, for example, in a range of 300 μm to 900 μm, andpreferably is 500 μm or less for high-density recording.

Information is recorded on the information layer 20. The informationlayer 20 is a multi-layer film in which a plurality of layers arestacked. The information layer 20 may include a lower side dielectriclayer 21, a lower side interface layer 22, a recording layer 23, anupper side interface layer 24, an upper side dielectric layer 25 and areflection layer 26 placed in this order from the first substrate 11side. The term “lower side” refers to the first substrate 11 side withrespect to the recording layer 23. The lower side interface layer 22 andthe upper side interface layer 24 are both inorganic layers.

The recording medium 10 shown in FIG. 1 is an example, and may haveanother configuration in some cases. For example, the lower sideinterface layer 22 also can function as the lower side dielectric layer21, and the upper side interface layer 24 also can function as the upperside dielectric layer 25. Therefore, the lower side dielectric layer 21and/or the upper side dielectric layer 25 can be omitted. Furthermore,the reflection layer 26 can be omitted. Furthermore, the reflectionlayer 26 may be composed of a combination of a plurality of layers.Furthermore, either one of the lower side interface layer 22 and theupper side interface layer 24 can be omitted.

In the recording medium 10, information is recorded/reproduced with thelaser beam 14 transmitted through the first substrate 11. Therefore, thematerial for the first substrate 11 preferably is almost transparent tothe wavelength of the laser beam 14. As the material for the firstsubstrate 11, polycarbonate resin, polymethylmethacrylate, polyolefinresin, norbornene resin, UV-curable resin, glass or an appropriatecombination of these materials can be used. The first substrate 11 has adisk shape. The thickness thereof is not particularly limited, and is,for example, in a range of 0.01 mm to 1.5 mm. In order to performhigh-density recording using an optical system with a high lensnumerical aperture (NA), the thickness of the first substrate 11preferably is 0.3 mm or less.

As the material for the lower side dielectric layer 21 and the upperside dielectric layer 25, for example, an oxide of an element such as Y,Ce, Ti, Zr, Nb, Ta, Co, Zn, Al, Si, Ge, Sn, Pb, Sb, Bi and Te can beused. Furthermore, a nitride of an element such as Ti, Zr, Nb, Ta, Cr,Mo, W. B, Al, Ga, In, Si, Ge, Sn and Pb also can be used. Furthermore, acarbide of an element such as Ti, Zr, Nb, Ta, Cr, Mo, W and Si also canbe used. Furthermore, a sulfide such as Zn or Cd sulfide, a seleniumcompound or a tellurium compound also can be used. Furthermore, afluoride such as Mg or Ca fluoride, or elemental C, elemental Si andelemental Ge also can be used. Alternatively, a mixture of thesematerials also can be used.

The lower side interface layer 22 and the upper side interface layer 24are adjacent to the recording layer 23, and are made of an inorganicsubstance. At least one interface layer (preferably both the interfacelayers) selected from the lower side interface layer 22 and the upperside interface layer 24 contains a nitride of Si_(x)Ge_(1-x) (where0.3≦x≦0.9, preferably 0.5≦x≦0.8) as its main component. Herein, tocontain as its main component refers to containing Si, Ge and N in aratio of 90 atomic % or more in total. The content of Si is preferablyin a range of 30 atomic % to 90 atomic %, more preferably in a range of50 atomic % to 80 atomic % so as to enhance the thermal stability andenvironment reliability such as moisture resistance, and decrease theextinction coefficient k to increase the transmittance. By enhancing thethermal stability of the interface layer, the durability in repeatedrecording can be enhanced, and by increasing the transmittance of theinterface layer, the recording sensitivity of the recording medium (inparticular, a multi-layer recording medium) can be increased.Furthermore, when nitrogen in the interface layer becomes insufficient,the effect of promoting the crystallization of the recording layer 23 isweakened. When nitrogen in the interface layer becomes excessive, theinterface layer is likely to peel off from the recording layer 23.Therefore, it is preferable that the amount of nitrogen in the interfacelayer is optimized in accordance with the contents of Si and Ge. Forexample, it is preferable that the concentration of nitrogen isminimized in a range where an erasure ratio of 30 dB or more can beobtained. The lower side interface layer 22 and the upper side interfacelayer 24 preferably contain Si, Ge and N in an atomic ratio ofSi:Ge:N=a:b:c (where 0.33≦a/(a+b)≦0.90 and 0.3≦c/(a+b+c)≦0.6, morepreferably 0.50≦a/(a+b)≦0.80 and 0.4≦c/(a+b+c)≦0.5).

The recording layer 23 is of a rewritable type in which information canbe rewritten any number of times or of a write-once type in whichinformation can be written in an unrecorded region only once. Therecording layer 22 is changed between at least two different states,which are discernable optically, by irradiation with a light beam(generally, a laser beam) incident from the first substrate 11 side. Inthe case where the recording layer 23 is of a rewritable type, a Te—Sbbased chalcogenide thin film, for example, a Ge—Sb—Te based alloy thinfilm or a Ge—Sn—Sb—Te based alloy thin film can be used. Furthermore, analloy thin film (e.g., Ag—In—Sb—Te based alloy or Ag—In—Ge—Sb—Te basedalloy) in which In, Ge, Au, Ag and the like are added to a eutecticcomposition of Sb—Te also can be used. These materials are changedreversibly between a crystal phase and an amorphous phase by irradiationwith the laser beam 14. In this case, the reflectance of a portion in acrystalline state is different from that of a portion in an amorphousstate. Therefore, both the states can be discriminated by irradiationwith the laser beam 14 for reproducing. Herein, the Ge—Sb—Te based alloyrefers to an alloy containing Ge, Sb and Te in an amount of 90 atomic %or more in total. Similarly, the Ge—Sn—Sb—Te based alloy refers to analloy containing Ge, Sn, Sb and Te in an amount of 90 atomic % or morein total. This also applies to the other alloys.

Among the above materials, in the case of using a Ge—Sb—Te based alloycontaining Ge in an amount of 30 atomic % or more (in particular, 40atomic % or more), or a Ge—Sn—Sb—Te based alloy containing Ge and Sn inan amount of 30 atomic % or more (in particular, 40 atomic % or more),an optical contrast between the crystal phase and the amorphous phasebecomes large, whereby a large C/N ratio is obtained. On the other hand,these materials undergo a large change in volume between the crystalphase and the amorphous phase, which results in a decrease in durabilitywith respect to repeated recording. Therefore, in the case of usingthese materials, it is more effective to enhance the durability withrespect to repeated recording by using an interface layer containing anitride of Si—Ge as its main component.

Furthermore, in the case where the recording layer 23 is of a rewritabletype, at least one element selected from O, N, F, C, S and B may beadded to a material for the recording layer 23 so as to adjust thethermal conductivity and optical constant or to enhance the heatresistance and environment reliability. These elements are added in anamount of 10 atomic % or less based on the total amount of the recordinglayer 23.

Furthermore, in the case where the recording layer 23 is of a rewritabletype, the recording layer 23 may include a layer formed of theabove-mentioned material and a crystallization promoting layer adjacentthereto.

In the case where the recording layer 23 is of a rewritable type, bysetting the thickness of the recording layer 23 to be 3 nm to 20 nm, asufficient C/N ratio (carrier to noise ratio) can be obtained. Bysetting the thickness of the recording layer 23 to be 3 nm or more,sufficient reflectance and reflectance change are obtained. Furthermore,by setting the thickness of the recording layer 23 to be 20 nm or less,heat diffusion in the recording layer 23 can be prevented from beingincreased excessively. Furthermore, in the case where the recordinglayer 23 is thin (for example, in the case where the thickness is 18 nmor less (in particular, 14 nm or less)), heat generated during recordingis likely to diffuse in a thickness direction of the recording layer 23,whereby time for the recording layer 23 to be held in the vicinity of acrystallization temperature is shortened. As a result, an erasure ratiois decreased. Therefore, in the case where the recording layer 23 isthin, it is more effective to increase an erasure ratio by using aninterface layer containing a nitride of Si—Ge as its main component.

In the case where the recording layer 23 is of a write-once type, as thematerial for the recording layer 23, a material containing Te, O(oxygen)and at least one element selected from Al, Si, Ti, V, Cr, Mn, Fe, Co,Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ru, Rh, Pd, Ag, In, Sn, Sb, Hf, Ta, WRe, Os, Ir, Pt, Au and Bi can be used. For example, the recording layer23 made of a material such as Te—O—Pd and Te—O—Au can be used. Therecording layer 23 made of these materials is irreversibly changed froman amorphous phase to a crystal phase by irradiation with the laser beam14 for recording. These two states can be discriminated by irradiationwith the laser beam 14 for reproducing. As the element M, Pd or Au isparticularly preferable since a sufficient crystallization speed andhigh environment reliability are obtained.

It is preferable that the content of oxygen in the write-once recordinglayer 23 is in a range of 25 atomic % to 60 atomic %, and the content ofthe element M therein is in a range of 1 atomic % to 35 atomic %. Bysetting the contents of oxygen and the element M in these ranges, asufficient C/N ratio is obtained. By setting the content of an oxygenatom in the recording layer 23 to be 25 atomic % or more, the thermalconductivity of the recording layer 23 can be prevented from beingincreased excessively to enlarge a recording mark. Furthermore, bysetting the content of an oxygen atom in the recording layer 23 to be 60atomic % or less, the following can be prevented: the thermalconductivity of the recording layer 23 is decreased excessively, andeven when a recording power is increased, a recording mark cannot beformed with a sufficient size. By setting the content of the element Min the recording layer 23 to be 1 atomic % or more, the function ofpromoting the growth of Te crystal during irradiation with laser lightcan be obtained sufficiently. As a result, the crystallization speed ofthe recording layer 23 can be set to be a sufficient value, and arecording mark can be formed at a high speed. Furthermore, by settingthe content of the element M in the recording layer 23 to be 35 atomic %or less, a reflectance change between an amorphous phase and a crystalphase can be increased, and a C/N ratio can be increased.

Furthermore, in the case where the recording layer 23 is of a write-oncetype, at least one element selected from N, F, C, S and B may be addedto a material for the recording layer 23 so as to adjust a thermalconductivity and an optical constant, or to enhance heat resistance andenvironment reliability. These elements are added in an amount of 10atomic % or less of the total amount of the recording layer 23.

In the case where the recording layer 23 is of a write-once type, bysetting the thickness of the recording layer 23 to be 5 nm to 70 nm, asufficient C/N ratio can be obtained. By setting the thickness of therecording layer 23 to be 5 nm or more, sufficient reflectance andreflectance change can be obtained. Furthermore, by setting thethickness of the recording layer 23 to be 70 nm or less, the heatdiffusion in the thin film surface of the recording layer 23 can be setto be an appropriate amount, and a satisfactory C/N ratio can beobtained even in high-density recording.

As the material for the reflection layer 26, for example, Au, Ag, Cu,Al, Ni, Pd, Pt, Bi, Sb, Sn, Zn, Cr or an alloy thereof can be used.Furthermore, as the reflection layer 26, a multi-layer film made of aplurality of dielectric layers having different refractive indices maybe used.

As the material for the second substrate 12, the same material as thatfor the first substrate 11 can be used. A material different from thatfor the first substrate 11 also may be used, and the material for thesecond substrate 12 may be opaque at the wavelength of the laser beam14. The thickness of the second substrate 12 is not limitedparticularly, and can be set in a range of about 0.01 mm to 3.0 mm.

Furthermore, the optical information recording medium of the presentinvention may include at least two information layers between the firstsubstrate 11 and the second substrate 12. FIG. 2 shows a partialcross-sectional view of an optical information recording medium 10 a(hereinafter, which may be referred to as a recording medium 10 a)including two information layers. In FIG. 2, hatching of a firstinformation layer 20 a and a second information layer 20 b is omitted.

The recording medium 10 a includes the first information layer 20 a, aseparation layer 27 and the second information layer 20 b placed in thisorder from the first substrate 11 side. At least one information layerstacked via an additional separation layer further may be formed betweenthe second information layer 20 b and the second substrate 12. Theseinformation layers include a recording layer, respectively, andinformation is recorded independently. At least one information layer ofthese information layers has a recording layer 23, a lower sideinterface layer 22 and/or an upper side interface layer 24 adjacent tothe recording layer 23, in the same way as in the information layer 20shown in FIG. 1. Each information layer is irradiated with the laserbeam 14 condensed by the objective lens 13 from the first substrate 11side, whereby recording/reproducing is performed.

The transmittance of the first information layer 20 a is required to beat least about 30%. The first information layer 20 a may be of arewritable type, a write-once type or a read-only type. The secondinformation layer 20 b may be of a rewritable type, a write-once type ora read-only type.

The separation layer 27 can be made of UV-curable resin or the like. Thethickness of the separation layer 27 is required to be equal to or morethan a depth of focus determined at least by the numerical aperture NAof the objective lens 13 and the wavelength λ of the laser beam 14 sothat when information is reproduced from either one of the firstinformation layer 20 a and the second information layer 20 b, crosstalkfrom the other becomes small. Furthermore, the thickness of theseparation layer 27 is required to be in a range in which light can becondensed in all the information layers. For example, in the case whereλ=405 nm and NA=0.85, the thickness of the separation layer 27 isrequired to be in a range of 5 μm to 50 μm.

In the recording medium 10 a including two information layers,information can be recorded independently in two information layers, sothat the recording density can be doubled.

Furthermore, the following also may be possible: two recording media asdescribed above are prepared, and the respective second substrates 12are attached to each other, whereby the amount of information that canbe accumulated in one medium further can be doubled.

In the optical information recording medium of the present invention,grooves, lands (flat portions between the grooves), or grooves and landscan be used as recording tracks. In the case where the wavelength oflaser light used for recording/reproducing is λ and the lens numericalaperture is NA, the recording medium can be increased in density bysetting the interval of the recording tracks to be λ/NA or less. Inparticular, it is preferable that the interval between recording tracksis 0.8 λ/NA or less.

Embodiment 2

In Embodiment 2, a method for producing the optical informationrecording medium described in Embodiment 1 will be described.

Each layer (excluding the separation layer 27) constituting theinformation layer of the recording medium can be formed by a generalvapor phase deposition method such as vapor deposition, sputtering, ionplating, CVD (Chemical Vapor Deposition), and MBE (Molecular BeamEpitaxy). Furthermore, the separation layer 27 can be formed by a methodfor applying a UV-curable resin by spin coating and irradiating theresin with UV-light to cure the resin, or by a method for attaching anadhesive sheet.

Hereinafter, a method for forming an interface layer (lower sideinterface layer 22 and/or upper side interface layer 24) containing anitride of SixGe1-x (where 0.3≦x≦0.9) as its main component will bedescribed. The interface layer can be formed by general sputtering orreactive sputtering. In the case of the reactive sputtering, a targetcontaining Si and Ge is sputtered in a sputtering apparatus (in anatmosphere containing inert gas and nitrogen gas) in which at leastinert gas and nitrogen gas flow. In the case of the general sputtering,a target containing a nitride of Si and Ge is sputtered in a sputteringapparatus (in an atmosphere containing inert gas) in which at leastinert gas flows. In both the cases, by setting the pressure of asputtering gas to be 0.5 Pa or more, the stress of a layer to be formedcan be alleviated. As a result, the tendency for peeling between therecording layer and the interface layer can be reduced. According tothis producing method, a recording medium with high environmentalreliability such as moisture resistance can be produced.

The recording medium can be produced by stacking the above-mentionedrespective layers on the first substrate 11, and forming the secondsubstrate 12 on the information layer or attaching the second substrate12 to the information layer. Alternatively, the recording medium can beproduced by stacking the above-mentioned respective layers on the secondsubstrate 12 and forming the first substrate 11 on the information layeror attaching the first substrate 11 to the information layer. The lattermethod is suitable in the case where the first substrate 11 is thin (0.4mm or less). According to the latter method, in the case where an unevenpattern (e.g., grooves for guiding a laser beam or address pits) areformed on the second substrate 12 and the separation layer 27, it isrequired to use the second substrate 12 and the separation layer 27 withan uneven pattern formed thereon. Such an uneven pattern can be formedby transferring the shape of a stamper with an even pattern formedthereon by an injection method. Furthermore, in the case where it isdifficult to form the uneven pattern by the injection method because asubstrate and a separation layer to be formed are thin, a 2P method(photo-polymerization method) can be used.

Embodiment 3

In Embodiment 3, a method for recording/reproducing information withrespect to the optical information recording medium described inEmbodiment 1 will be described.

FIG. 3 schematically shows an exemplary configuration of arecording/reproducing apparatus used in the recording method of thepresent invention. A recording/reproducing apparatus 30 in FIG. 3includes a laser diode 31, a half mirror 32, a motor 33, a photodetector34 and an objective lens 13. In the recording/reproducing apparatus 30,information is recorded/reproduced with respect to the recording medium35. The recording medium 35 is rotated by the motor 33. The recordingmedium 35 is the optical information recording medium of the presentinvention described in Embodiment 1.

The laser beam 14 emitted from the laser diode 31 is transmitted throughthe half mirror 32 and the objective lens 13 to be focused onto therecording medium 35. Information is recorded by irradiating therecording medium 35 with the laser beam 14 with a particular power.Information is reproduced by irradiating the recording medium 35 withthe laser beam 14 of particular power and detecting the light reflectedfrom the recording medium 35 by the photodetector 34.

An information signal is recorded by forming a recording mark on arecording layer. For example, a recording mark is formed by changing therecording layer to a state having different optical characteristics byirradiation with pulse light modulated between a power level P1 and apower level P3 smaller than the power level P1. The intensity of a lasercan be modulated easily by modulating a driving current of the laserdiode 31. Furthermore, the intensity of a laser also can be modulated byusing means such as an electrooptical modulator and an acoustic opticalmodulator.

A recording mark (in an amorphous phase) can be formed by irradiating aportion of the recording layer in a crystal phase with a laser beamhaving a single rectangular pulse of the peak power P1. However, in thecase of forming a long recording mark, it is preferable to use arecording pulse train composed of a plurality of modulated laser pulsesso as to prevent overheating and make the width of the recording markuniform. FIG. 4 shows an example of such a recording pulse train. InFIG. 4, the horizontal axis represents time, and the vertical axisrepresents a power of a laser beam. In this pulse train, first, a partof the recording layer is irradiated alternately with a laser pulse of apeak power P1 and a laser pulse of a bottom power P3 (P3<P1) to bechanged from a crystal phase to an amorphous phase, whereby a recordingmark is formed. At the trailing edge of the pulse train, a coolingsection for irradiation of a cooling power P4 (P4<P3) may be provided,as shown in FIG. 4. A portion where a recording mark is not to be formedand a portion where a recording mark is to be erased are irradiated witha laser beam (continuous light) kept constant at a bias power P2(P2<P1). In the case of forming a recording mark, it is preferable thatas the recording mark becomes longer, the number of pulses of a laserpulse is increased.

According to the method for recording/reproducing information withrespect to the optical information recording medium,recording/reproducing may be performed at a linear velocity varieddepending upon a region. When a recording mark is formed using at leasttwo different linear velocities, as the linear velocity becomes higher,each power level preferably is set so as to increase a ratio of P3/P1 ora ratio of P3/P2. Because of this, in the case where a recording mediumis stored in a high-temperature environment, a decrease in a signalamplitude of a recording mark and difficulty in erasing a recording markcan be prevented.

Herein, due to the difference in a recording pattern determined by thelength of a recording mark, the lengths of spaces before and after therecording mark and the length of an adjacent recording mark, mark edgepositions become nonuniform, which may cause an increase in jitter.According to the recording/reproducing method of the present invention,in order to prevent the nonuniformity of mark edge positions to reducejitter, the position or length of each pulse in the above-mentionedpulse train is adjusted and compensated so that edge positions arealigned on the pattern basis.

In the case of reproducing the information signal thus recorded, arecording medium is irradiated with continuous light of a power level Pr(Pr<P1), light reflected from the recording medium is detected by thephotodetector 34, and a change in the amount of reflected light isoutput as a reproducing signal.

EXAMPLES

Hereinafter, the present invention will be described more specificallyby way of examples. The present invention is not limited by thefollowing examples.

Example 1

In Example 1, a recording medium of the present invention including onlyone information layer will be described. In Example 1, a plurality ofsamples with a varying ratio of Si and Ge in an interface layer wereproduced, and evaluated mainly for durability and environmentreliability in repeated recording.

The samples were produced as follows. As a protection substrate (secondsubstrate 12), a substrate (diameter: about 12 cm; thickness: about 1.1mm) made of polycarbonate resin with grooves (groove pitch: 0.32 μm;groove depth: about 20 nm) formed on one side was used.

An information layer was formed, by sputtering, on the surface of theprotection substrate with the grooves formed thereon. First, areflection layer (thickness: about 160 nm) made of Ag—Pd—Cu was formedwhile Ar gas was allowed to flow, using a target made of Ag—Pd—Cu(atomic ratio: 98:1:1). Then, an upper side interface layer (thickness:about 15 nm) made of Si—Ge—N was formed while Ar and N₂ gases wereallowed to flow, using a target made of Si—Ge. A recording layer(thickness: about 10 nm) made of Ge—Sb—Te was formed while Ar and N₂gases (flow ratio: 98:2) were allowed to flow, using a target made ofGe—Sb—Te (atomic ratio: 22:23:55). A lower side interface layer(thickness: about 5 nm) made of Si—Ge—N was formed while Ar and N₂ gaseswere allowed to flow, using a target made of Si—Ge. A lower sidedielectric layer (thickness: about 55 nm) made of ZnS—SiO₂ was formedwhile Ar gas was allowed to flow, using a target made of ZnS—SiO₂ (moleratio: 80:20).

A sheet with a diameter of about 12 cm made of polycarbonate resin wasattached to the surface of the information layer thus formed viaUV-curable resin and was irradiated with UV-light to cure the resin.Thus, a first substrate having a thickness of about 0.1 mm was formed.

In Example 1, in order to change a ratio of Si and Ge in the interfacelayer, the content of Si in the Si—Ge target was varied as follows: 100atomic % (elemental Si), 90 atomic %, 80 atomic %, 67 atomic %, 50atomic %, 33 atomic %, 20 atomic %, 10 atomic %, 0 atomic % (elementalGe), whereby disks A1, B1, C1, D1, E1, F1, G1, H1 and I1 were produced.The ratio (% by volume) of nitrogen in sputtering gas was minimized sothat peeling from the recording layer did not occur in a range where 30dB or more of erasure ratio, measured by a method described later, wasobtained in each Si—Ge composition ratio. Furthermore, the compositionof the upper side interface layer was set to be the same as that of thelower side interface layer.

Table 1 shows the content of nitrogen in the optimized sputtering gasand the composition ratio of a target. Table 1 also shows the resultobtained by producing a single film of Si—Ge—N under the above conditionand measuring the optical constant (refractive index n and extinctioncoefficient k) at a wavelength of 405 nm.

TABLE 1 Content of Optical constant of Si—Ge—N Composition of targetnitrogen film (wavelength: 405 nm) Si [at %] Ge [at %] (% by volume) n k100 0 14 1.90 0.01 90 10 18 2.03 0.02 80 20 22 2.12 0.03 67 33 26 2.170.05 50 50 30 2.33 0.07 33 67 34 2.40 0.12 20 80 38 2.41 0.16 10 90 402.44 0.17 0 100 42 2.45 0.20

As shown in Table 1, as the content of Si in the target was higher, therefractive index n and the extinction coefficient k became small. Theatomic ratio between Si and Ge in the interface layer to be formed isessentially the same as that between Si and Ge in the target.

The grooves on each of the above-mentioned disks were irradiated with alaser beam with a wavelength of 405 nm condensed by a lens with anumerical aperture NA of 0.85, whereby single signals of 12.2 MHz and3.3 MHz were recorded alternately. Recording was performed while thedisk was being rotated at a linear velocity of 4.5 m/sec. Recording wasperformed by irradiation with a rectangular pulse modulated between apeak power P1 and a bias power P2. In the case of recording a signal of12.2 MHz, a single pulse (pulse width: 13.7 ns) was radiated. In thecase of recording a signal of 3.3 MHz, a pulse train composed of aleading pulse (pulse width: 20.5 ns) and subsequent 8 sub-pulses (width:6.9 ns; interval: 6.9 ns) was radiated. The reproducing power Pr was setto be 0.4 mW.

Under the above condition, the signal of 12.2 MHz and the signal of 3.3MHz were recorded alternately onto unrecorded tracks ten times in total.Then, a C/N ratio in the case of recording the signal of 12.2 MHz on theresultant disk was measured by a spectrum analyzer. Furthermore, thesignal of 3.3 MHz was recorded on the resultant disk, and an erasureratio, i.e., an extinction ratio of an amplitude of 12.2 MHz wasmeasured by a spectrum analyzer. Measurement was conducted by changingP1 and P2 arbitrarily. P1 was set to be a power that was 1.3 times thepower at which the amplitude became lower by 3 dB compared with themaximum, and P2 was set to be the central value in a power range wherethe erasure ratio exceeded 25 dB.

In any of the disks, the set power of P1 was about 6.2 to 6.8 mW, theset power of P2 was about 2.2 to 2.4 mW, the C/N ratio at these setpowers was about 53 to 54 dB, and the erasure ratio was about 30 to 32dB. These initial characteristics were almost the same in each disk.

Next, in order to check the durability over plural repeated recordings,the signals of 12.2 MHz and 3.3 MHz were repeatedly recorded alternatelyat the respective set powers with respect to each disk, and the C/Nratio and the erasure ratio were measured in the same way as in theabove. Then, the number of recordings where a decrease in a C/N ratiowas equal to or less than 1 dB and a decrease in an erasure ratio wasequal to or less than 3 dB was defined as the repeatedly recordablenumber of times. Table 2 shows the result.

TABLE 2 Composition Repeatedly recordable Time of of target number oftimes occurrence Disk Si Ge Wavelength Wavelength of peeling No. [at %][at %] 405 nm 660 nm [hour] A1 100 0 10,000 or more 10,000 or more □100B1 90 10 10,000 or more 10,000 or more 200–500 C1 80 20 10,000 or more10,000 or more 500□ D1 67 33 10,000 or more 10,000 or more 500□ E1 50 5010,000 or more 10,000 or more 500□ F1 33 67 About 5,000 10,000 or more500□ G1 20 80 About 2,000 10,000 or more 200–500 H1 10 90 About 80010,000 or more 200–500 I1 0 100 About 300 10,000 or more 200–500

Furthermore, 9 kinds of disks with a varying Si—Ge ratio were producedin the same way as in the disks A1 to I1, except that the groove pitchof the substrate was set to be 0.53 μm, the groove depth was set to be35 nm, the thickness of the ZnS—SiO₂ lower side dielectric layer was setto be 140 nm and the thickness of the Si—Ge—N upper side interface layerwas set to be 25 nm. Regarding these 9 kinds of disks, the repeatedlyrecordable number of times was checked under the same condition as theabove, except that the wavelength of a laser beam was set to be 660 nm,the frequency of a recording signal was set to be 9.0 MHz and 2.4 MHzand the reproducing power Pr was set to be 0.7 mW. Table 2 shows theresult.

Furthermore, in order to check the environment reliability (inparticular, moisture resistance) of the disks A1 to I1, the disks werestored for a long period of time in an environment of a temperature of90° C. and a humidity of 80% RH, whereby the time of the occurrence ofpeeling was measured. Table 2 also shows the result. In Table 2, “≦100”represents 100 hours or less, “200–500” represents a range of 200 hoursto less than 500 hours, and “500 ≦” represents that peeling did notoccur even after the elapse of 500 hours or more.

As shown in Table 2, in the disk I1 including the interface layer madeof Ge—N, the repeatedly recordable number of times at a wavelength of405 nm was about several hundred times. However, as the compositionratio of Si was increased, the repeatedly recordable number of times wasincreased. In the case of Si of 50 atomic % or more, repeated recordingof 10,000 times or more was possible. In contrast, the repeatedlyrecordable number of times was 10,000 or more even in any disk at awavelength of 660 nm. It was found from this result that each thin filmwas likely to be thermally damaged when the wavelength became shorter.Furthermore, the durability was enhanced by increasing the compositionratio of Si in the interface layer.

Furthermore, in the disk A1 using the interface layer made of Si—N,peeling occurred within 100 hours. In the disk I1 using the interfacelayer made of Ge—N, peeling occurred after the elapse of 200 hours. Bysetting Si and Ge in an appropriate ratio, e.g., setting the ratio of Sito be about 80 to 30 atomic %, the moisture resistance was enhancedremarkably, and stable moisture resistance was exhibited over 500 hoursor more.

As described above, by using an inorganic layer containing a nitride ofSi_(x)Ge_(1-x) (where 0.3≦x≦0.9) as its main component, an opticalinformation recording medium excellent in durability in repeatedrecording using violet laser light and environment reliability wasobtained.

Example 2

In Example 2, the optical information recording medium of the presentinvention including a plurality of information layers will be described.In Example 2, a plurality of samples with a various ratio of Si and Gein an interface layer were produced, and evaluated mainly fortransmittance and recording sensitivity.

The samples were produced as follows. As a protection substrate (secondsubstrate 12), a substrate (diameter: about 12 cm; thickness: about 1.1mm) made of polycarbonate resin with grooves (groove pitch: 0.32 μm;groove depth: about 20 nm) formed on one side was used.

A second information layer was formed by sputtering on the surface ofthe protection substrate with the grooves formed thereon. First, areflection layer (thickness: about 160 nm) made of Ag—Pd—Cu was formedwhile Ar gas was allowed to flow, using a target made of Ag—Pd—Cu(atomic ratio: 98:1:1). Then, a reflection layer (thickness: about 10nm) made of Al—Cr was formed while Ar gas was allowed to flow, using atarget made of Al—Cr (atomic ratio: 98:2). An upper side dielectriclayer (thickness: about 15 nm) made of ZnS—SiO₂ was formed while Ar gaswas allowed to flow, using a target made of ZnS—SiO² (mole ratio:80:20). An upper side interface layer (thickness: about 5 nm) made ofSi—Ge—N was formed while Ar and N₂ gases were allowed to flow, using atarget made of Si—Ge. A recording layer (thickness: about 12 nm) made ofGe—Sb—Te was formed while Ar and N₂ gases (flow ratio: 98:2) wereallowed to flow, using a target made of Ge—Sb—Te (atomic ratio:22:23:55). A lower side interface layer (thickness: about 5 nm) made ofSi—Ge—N was formed while Ar and N₂ gases were allowed to flow, using atarget made of Si—Ge. A lower side dielectric layer (thickness: about 50nm) made of ZnS—SiO₂ was formed while Ar gas was allowed to flow, usinga target made of ZnS—SiO₂ (mole ratio: 80:20).

The surface of the information layer thus formed was coated withUV-curable resin, and the same groove pattern as that on the protectionsubstrate was transferred to the surface coated with UV-resin by theabove-mentioned 2P method. Thus, a separation layer (thickness: about 20μm) with the grooves formed on the surface was formed.

A first information layer was formed by sputtering on the surface of theseparation layer. First, a reflection layer (thickness: about 10 nm)made of Ag—Pd—Cu was formed while Ar gas was allowed to flow, using atarget made of Ag—Pd—Cu (atomic ratio: 98:1:1). Then, an upper sideinterface layer (thickness: about 10 nm) made of Si—Ge—N was formedwhile Ar and N₂ gases were allowed to flow, using a target made ofSi—Ge. A recording layer (thickness: about 6 nm) made of Ge—Sb—Te wasformed while Ar and N₂ gases (flow ratio: 98:2) were allowed to flow,using a target made of Ge—Sb—Te (atomic ratio: 22:23:55). A lower sideinterface layer (thickness: about 5 nm) made of Si—Ge—N was formed whileAr and N₂ gases were allowed to flow, using a target made of Si—Ge. Alower side dielectric layer (thickness: about 45 nm) made of ZnS—SiO₂was formed while Ar gas was allowed to flow, using a target made ofZnS—SiO₂ (mole ratio: 80:20).

A sheet with a diameter of about 12 cm made of polycarbonate resin wasattached to the surface of the first information layer thus formed viaUV-curable resin and was irradiated with UV-light to cure the resin.Thus, a transparent substrate (first substrate) having a thickness ofabout 0.09 mm was formed.

In Example 2, in order to change a ratio of Si and Ge in the interfacelayer, the content of Si in the Si—Ge target was varied as follows: 100atomic % (elemental Si), 90 atomic %, 80 atomic %, 67 atomic %, 50atomic %, 33 atomic %, 20 atomic %, 10 atomic %, 0 atomic % (elementalGe), whereby disks A2, B2, C2, D2, E2, F2, G2, H2 and I2 were produced.The concentration of nitrogen in sputtering gas was set to be the sameas that in Example 1. Furthermore, in each information layer, thecomposition of the upper side interface layer was set to be the same asthat of the lower side interface layer.

Herein, in order to check the transmittance of the first informationlayer in each disk, a multi-layer film having the same configuration asthat of the first information layer was formed on a quartz substrate,and the transmittance was measured by a spectroscope. Table 3 shows thetransmittance at a wavelength of 405 nm.

TABLE 3 Composition of target Transmittance of first Set power of secondDisk Si Ge information layer information layer No. [at %] [at %] [%] P1[mW] P2 [mW] A2 100 0 50 10.2 3.4 B2 90 10 48 10.5 3.5 C2 80 20 47 11.13.7 D2 67 33 46 11.4 3.8 E2 50 50 45 11.9 4.0 F2 33 67 44 12.7 4.2 G2 2080 42 13.5 4.5 H2 10 90 41 14.9 5.0 I2 0 100 40 15.5 5.2

As shown in Table 3, as the composition ratio of Si was larger, thetransmittance of the first information layer was higher, which reflectedthe values of the extinction coefficient k shown in Table 1.

The grooves on the first and second information layers of each of theabove-mentioned disks were irradiated with a laser beam with awavelength of 405 nm condensed by a lens with a numerical aperture NA of0.85, whereby single signals of 12.2 MHz and 3.3 MHz were recordedalternately. Recording was performed while the disk was being rotated ata linear velocity of 5 m/sec. Recording was performed by irradiationwith a rectangular pulse modulated between a peak power P1 and a biaspower P2. In the case of recording a signal of 12.2 MHz, a single pulse(pulse width: 13.7 ns) was used. In the case of recording a signal of3.3 MHz, a pulse train composed of a leading pulse (pulse width: 20.5ns) and subsequent 8 sub-pulses (width: 6.9 ns; interval: 6.9 ns) wasused. The reproducing power Pr was set to be 0.7 mW.

Under the above condition, the signal of 12.2 MHz and the signal of 3.3MHz were recorded alternately onto unrecorded tracks ten times in total.Then, a C/N ratio in the case of recording the signal of 12.2 MHz on theresultant disk was measured by a spectrum analyzer. Furthermore, thesignal of 3.3 MHz was recorded on the resultant disk, and an erasureratio, i.e., an extinction ratio of an amplitude of 12.2 MHz wasmeasured by a spectrum analyzer. Measurement was conducted by changingP1 and P2 arbitrarily. P1 was set to be a power that was 1.3 times thepower at which the amplitude became lower by 3 dB compared with themaximum, and P2 was set to be the central value in a power range wherethe erasure ratio exceeded 25 dB.

In the first information layer of any of the disks, the set power of P1was about 8.8 to 9.4 mW, the set power of P2 was about 3.4 to 3.6 mW,the C/N ratio at these set powers was about 52 to 53 dB, and the erasureratio was about 30 to 32 dB. These initial characteristics were almostthe same in each disk.

In the second information layer, the C/N ratio at the set powers wasabout 53 to 54 dB, and the erasure ratio was about 30 to 32 dB, whichwere almost the same in each disk. However, the set powers of P1 and P2in the second information layer were varied depending upon the disk.Table 3 shows the set power in the second information layer.

As shown in Table 3, in the disk I2 using the interface layer made ofGe—N, the set power of P1 in the second information layer was 15 mW ormore. The set power of P1 was decreased as the composition ratio of Siwas increased. When the composition ratio of Si was 50 atomic % or more,the set power of P1 was 12 mW or less.

Thus, in the case of recording information with respect to a recordingmedium including a plurality of information layers with violet laserlight, by using an inorganic layer containing a nitride ofSi_(x)Ge_(1-x) (where 0.3≦x≦0.9) as its main component, recording can beperformed with light of lower power.

INDUSTRIAL APPLICABILITY

As described above, according to the present invention, an opticalinformation recording medium capable of recording/reproducinginformation with satisfactory reliability even in recording/reproducingwith light beam having a short wavelength or in recording/reproducingwith respect to a plurality of information layers, and a recordingmethod using the same. The present invention is applicable to variousoptical information recording media.

1. An optical information recording medium, comprising: a firstsubstrate; a second substrate disposed in parallel with the firstsubstrate; a first information layer disposed between the firstsubstrate and the second substrate; and a second information layerdisposed between the first information layer and the second substrate,wherein the first information layer comprises a phase-change recordinglayer and an inorganic layer directly adjacent to the phase-changerecording layer, the phase-change recording layer is changed between atleast two different states, which are discernable optically, byirradiation with a light beam incident from the first substrate side,the phase-change recording layer is made of an alloy containing Te andSb, and the inorganic layer contains a nitride of Si_(x)Ge_(1-x) (where0.3≦x≦0.9) as a main component.
 2. An optical information recordingmedium according to claim 1, wherein the phase-change recording layer ischanged reversibly between the at least two different states, which arediscernable optically, by irradiation with the light beam.
 3. An opticalinformation recording medium according to claim 1, wherein thephase-change recording layer is changed between the different states bya light beam with a wavelength of 500 nm or less.
 4. An opticalinformation recording medium according to claim 1, wherein the firstinformation layer includes a reflection layer disposed on the secondsubstrate side with respect to the phase-change recording layer.
 5. Anoptical information recording medium according to claim 1, wherein athickness of the phase-change recording layer is 18 nm or less.
 6. Anoptical information recording medium according to claim 1, wherein thephase-change recording layer is made of a Ge—Sb—Te based alloy, aGe—Sn—Sb—Te based alloy, an Ag—In—Sb—Te based alloy or an Ag—In—Ge—Sb—Tebased alloy.
 7. An optical information recording medium according toclaim 1, wherein the phase-change recording layer is made of a Ge—Sb—Tebased alloy, and the alloy contains Ge in a content of 30 atomic % ormore.
 8. An optical information recording medium according to claim 1,wherein the phase-change recording layer is made of a Ge—Sn—Sb—Te basedalloy, and the alloy contains Ge and Sn in a content of 30 atomic % ormore in total.